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(NoModeL) G. F. DURANT & H. L. BAILEY. C. A. BAILEY, Admihistratrix ofH. L.. BAILEY, deceased.

- TELEPHONE EXCHANGE SYSTEM. No. 394,914. Patented Dec. 18, 1888.

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N. PETERS Phokohlhognpher. wasmn m'. n. c.

Nirnn STATES rricE.

'ATENT GEORGE F. DFRANT, OF ST. LOUIS, MISSOURI, AND HENRY L. BAILEY, OF

BROOKLYN, NE YORK; CORNELIA HENRY L BAILEY, DECEASED.

A. BAILEY ADMINlSTR-ATRIX OF TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 394,914, dated December18, 1888.

Application filed May 10, 1888. Serial No. 273,423. (No model.)

To aZZ whom it may concern:

3e it known that we, GEORGE E. D URANT, a citizen of the United States,residing at St. Louis, in the State of Missouri, and HENRY L. 5 BAILEY,a citizen of the United States, residing at Brooklyn, in Kings county,and State of New York, have invented certain new and useful Improvementsin Preventing Induction in Telephone- Lines and in Telephone-EX- changeSystems, of which the following is such a full, clear, and exactdescription as will enable any one skilled in the art to which itappertains to make and use the same, reference being had to theaccompanying drawings, forming part of this specification.

The object of our invention is to diminish the ringing induction intelephone-lines, and also to indicate to the operator at the centraloffice that the lines are busy, or that a line is connected with anotherline, or to indicate that the subscriber has failed to replace thetelephone on his hook, all of which give the busy test. Telephone-linesas they leave the central stat-ion are for considerable distance 5 inthe neighborhood of other telephone-lines, so that when a fluctuation ofcurrent takes place in one wire it induces currents in the neighboringwire or wires, and thus interferes with the operation and functions ofthese line-wires. The most serious induction is caused when ringingsubscribers up, for by the contrivances now employed when thesubscribers bell rings the circuit of his line is made and broken by hisbell-magnet, so that the current on his line rises from and falls tozero-as said bell vibrates. This gives rise to a great fluctuation ofcurrent and causes serious induction in neighboring wires, which 40induction seriously interferes with their operation. So, too, some linesbeing short and some long, when the same battery is used to ring upthese different lines a battery that would produce sufficient current inthe long line to ring the subscribers bell would produce a strongcurrent in the short line, so that when the short line is made andbroken by the rheotome-bell the fluctuation of current is between muchwider limits, for the bound together in a strand, or are arrangedstrength of it varies in this case from zero to the inscreased strengthjust spoken of.

Our invention consists, first, in making the resistance of the variouslines substantially equal within certain limits, so as to remove thisincreased inductive effect just alluded to, 5 5 and in using inconnection with said equalized lines a bell-magnet with a shunt, so thatthe magnet will not make and break the circuit, but merely cut in andcut out its own resistance.

Our invention consists, secondly, in providing the operators at thecentral station of a telephone-exchange system having equalized linesand bell-magnets, as described, with an arrangement ofsignaling-circuits and circuitcontrollers, that said operators at thecentral station may know when any line is in use or not left in itsnormal condition.

\Ve will describe our invention as applied to a system known as the Lawtelephone system, shown and described in Patents Nos. 220,8'7-i,225,797, 278,613, 294,851, and 319,856. e would here remark, however,that our invention could be used with other forms of switclrboard thanthe Law.

\Ve will now describe our invention in detail by referring to theaccompanying drawings, making a part of this specification.

Figure I is a diagrammatic view of a central office provided with theLaw switch-board having our invention applied thereto and thetelephone-lines radiating therefrom provided with our otherimprovements. Fig. II is a section of our non-inductive resistancesignaling-plug. 8 5

The same letters of reference indicate the same or corresponding partsthroughout the drawings.

A, B, O, and D designate four sections of a Law switch-board. At thecenter of said sec- 0 tions is left a space for the flexible connections. Some of these flexibleconnections we have shown diagrammaticallyat the center of. the different sections by black dots. The fixedterminals of the subscribers we have indicated diagrammatically by smallcircles to distinguish them from the flexible terminals.

In the switch-board we have shown a series of lines passing therethroughand represented a fixed terminal of each line in each section of theswitch-board. One flexible terminal of each line occurs in itsrespective section of the switch-board, the flexible terminal beingrepresented as connected with the wirespassing through the switch-boardby dotted lines. This is the Law switch-board, and will be understood byreference to the foregoing patcuts.

1 2 3' i 4 5 5 are the series of telephonelines passing through theboard and extending to the subscribers S, S S, S", S, S, S and Sconnected, respectively, to said lines.

Each subscriber is provided with a subscribers outfit, as represented inthe diagram, consisting of a bell, a bellanagnet, a telephonereceiver,and atransmitter. The receiver and transmitter are arranged so as to beplaced in the main circuit of each line when the telephone is taken offthe hook. lVhen the telephone is on its hook, the transmitter andreceiver are short-circuited to ground by way of said hook and a secondcontact, m, against which the hook is held by the weight of thetelephone, the same as in the case of the contact r. Each receivernormally hangs upon a springaetuated hook of any suitable construction.Two terminals, i, of the primary circuit of the transmitter arepreferably arranged above the telephone-hook, so that when the telephoneis removed therefrom the hook will be placed in the contact with saidterminals and complete the primary circuit of the transmitter. Thesefeatures make no part of our invention. In the old construction thebell-magnet, when a subscriber is signaled, makes and breaks the maincircuit, cutting in and cutting out the magnet. This, as pointed outabove, causes the current on. the line to varyfrom zero to its normalstrength, so that it will induce currents in neighboring wires, causingserious interterenee with telephone service. To obviate this, we arrangea shunt, 3, around the bell-magnet. The shunt completed. in the firstinstance by the armature of the bell magnet comin against a contact, q,arranged near said armature. The shunt is connected to ground by way ofthe telephone-hook, which normally rests against a contact, r, againstwhich the phone-hook is held by the weight of the receiver. \Vhen thetelephone is removed from the hook, the spring will draw the hookbackward and break the circuit of the shunt. 'When, however, the hook isin its normal position against the contact 4* and a signal is sent overthe line, the shunt will be alternately made and broken at the contactq, and thus the bell-magnet only will be cut in and cut out of circuit,the main circuit always remaining intact. Let us say, for instance, thatthe maincircuit resistance is two hundred ohms and the bell-magnetthirty-five ohms. If this circuit is made and broken, the resistancewill vary the full quantity of two hundred and thirty-five ohms. Thiswill cause serious induetion in neighboring wires. By our arrangementthe resistance of the magnet only is cut in and cut out of circuit, thusmaking in the instance supposed a variation of thirtyfive ohms asagainst two hundred and thirtyfive ohms by the old arrangemei'it. Thisof itself would greatly diminish ringing-induction in telephone-linesand result in a great benefit to the service.

The lines represented in the diagram are supposed to be of ditierentlengths, and are preferably grounded at each subscriber; but a completemetallic circuit could be used as well. In signaling subscribers in theLaw and other systems a battery common to all operators is used, orindependent batteries all of substantially equal. strength. In signalingover short lines, therefore, a strong current will be thrown upon theline, and when na ling a long line with the same battery a comparativelyweak current will be thrown upon the line. The battery or batteries ofcourse have to be made of such capacity that they can signal the longline, and when so made and used upon a short line it will cause in saidlatter line a stronger current than desired, and one which whensubjected to linetuations will set up strong induced currents inneighboring wires. So it is obvious that by using our shunt bell-magnetthe dillieulties, although greatly diminished, would not be entirelyremoved. \Ve therefore combine with this arrangement of ours anotherffil' ture which constitutes another part of our invention, which ispeculiarly adapted to our shunt-magnet. This feature consists of anon-inductive resistance, R, which is placed in the various lines, so asto make the resistance of all of them practically equal within certainlimits, so that the variation of current caused by signaling a line oflow resistance and a line of high .rcsistam'ee is obviated. Thisnon-inductive resistan cc may consist of a coil of w i re which is woundback upon itself, so as to pre vent the self-induction of the coilsthereof upon one another. The non-ind uctive resistance may be placed atthe subscribens end of the line or at the central office, or at anypoint intermediate thereof. The resistance of the lines by this meansmay be made absolutely the same, or can be practically made to varybetween certain limits only. This non-inductive resistance can be placedin the operators signaling-plug, if desired. The plug, which shown indetail in Fig. ll, could in this instance have the non-imluetivcresistance arranged within the shell. P, thebattenv being coi'lneeted tothe terminal a", which is in electrical communication with one end ofthe non-inductive coil, the other end of said coil being connected withthe signaling-ti p y. This signaling-tip 1 is made to reciprocate in theplug P, and is held in its normal position by a spiral spring, .2, whichis arranged within said plug. The tip l/ is eX- tended in the plug andterminates a short distance from but just opposite to the batteryterminal \Vhen signaling a short line, the

ICC

operator would merely touch the terminal of said line with the tip 1 Theresistance R would therefore be inserted in the line and bring theresistance of the short line up to or near a circuit standard. \Vhen along lineis to be signaled, the operator would insert the tip 1 into theterminal of said line and press down thereupon, which would bring theextension of the tip 3/ into contact with the terminal. .r and cut outthe non-inductive resistance. In the Law or other systems the lines areso numbered and arranged in the switchboard that the operators know bythe location thereof, or by the numbers, that the line is a long orshort one, so they are enabled to shortcircuit or leave the resistance Rin circuit. The signaling-plug P could be arranged in various ways so asto graduate the resistance thereof. The device shown in the drawings anddescribed in detail illustrates but one way of carrying out this featureof our invention.

Passing around the switch-board at the central oifice to each of thesubscribers thereof is a signaling-circuit, N, which is grounded orconnected with the return-circuit emanating from each subscriber. Inthis circuit is connected a battery, 0. The operators signaling-plugs Pare preferably connected in multiple arc with said battery, and to servethis purpose the battery 0 should be made of very low internalresistance, so that several lines could be signaled at the same timewithout causing appreciable variation in the current. Said battery maypreferably be an accumulator or storage-battery, which is well adaptedfor this purpose. Indepemlent signaling-batteries of uniform strengthcould be used by each operator, if desi red, but the multiple-arcarrangeimmt is preferred. The signaling-plugs are connected with thecircuit N by a split circuit havin two branches, in one of whichbranches is arranged a small telephone, which is positioned near the earof the operator. In the diagram we have shown two such telephones toeach. section (designated a I u l) b, &c., respectively) that is to s:y, there would be two operators, one upon each side of each section ofthe switch-board. In the other branch of the split circuit is arranged amagnet, Z, the armature of which is in the circuit of the other branchof the split circuit. The action of the magnet I when abnormallyenergized is to draw down its armature and break the circuit of the headtelephone, which we will hereinafter denominate the telephone -buzzer.The Law system is provided with a buzzer corresponding in functions tothe telephonebuzzer we have described, the purpose of which is toindicate that a line is busy. This is fully set forth in Patent- No.319,856 above, the arrangement in said patent being such that thesubscriber when he lifts the telephone from his hook cuts thebell-magnet out of circuit, so that when an operator in another sectiontouches the terminal of said subscriber her buzzer, which responds tothe vibration of the bell, fails to give forth any sound, which meansthat the line is busy, for when the telephone is on the hook and theline in'its normal condition her buzzer would vibrate in response to thesubscribers bell vibrations, which indicates that the line desired isnot busy. In our arrangement, the bell-magnet being always in circuit,some means has to be devised to indicate not busy when two lines areconnected. This is the purpose of the split circuit and magnet Z. Ourarrangement also indicates that a line is not in its normal condition,the same as the Law system, and when any line is not in its normalcondition our arrangement, as well as the Law, gives the signalof busy.For the successful operation of the system a line that is not in itsnormal condition, whether it. be connected or unconnected with any otherline, is considered busy.

The diagram shows the system under all possible'conditions.

Before describing in detail the operation of the system it may be wellin passing to state that the Law system is provided with call-circuitsthat are independent of the talking-circuits. In the diagram in theaccompanying drawings the talking-circuits only are shown. A subscriberin the Law system calls over the call-circuit to the operator at thecentral office, and before the operator at the central office connectsthe flexible terminal of the talkingcircuit of the calling subscriberwith the talking-circuit of the'cal led subscriber she touches the fixedterminal of the called subscriber with her signaling plug. This signalsthe called subscriber and notifies him that he is wanted, and at thesame time serves to tell the operator whether the called subscriber isbusy. If she gets a notbusy test, she makes the connection but if shegets a busy test by so signaling the called sub scriber she notifies thecalling subscriber that the line wanted is busy. Each subscriber in theLaw system also is provided with an individual talking-wire. Thesematters are alluded to herein so as to make the present system readilyun derstood, the details of the same being fully described in thepatents set out above:

First. The line 1 is represented in its normal condition and theoperator at Z) is represented as signaling such line by touching itsterminal in her section, of the switch-board with her plug. This sends acurrent over the line 1, said current passing by both branches of thesplit circuit to the signaling-plug, and from thence over the linethrough the bellmagnet and to ground, returning to the battery. The bellof the subscriber S will vibrate, the shunt-circuit thereof will be madeand broken, and the variation of resistance, caused by the cutting inand cutting out of the bell-magnet, will set up in the telephonebuzzerZ) a series of vibrations, which will indicate to said operator that theline 1 is not ily to changes in the line.

busy-that is, is in its normal condition. It maybe here remarked thatthe buzzer-telephones are made insensitivethat is, sluggish in aetionsoas not to respond too read- The current which passes through its branchof the circuitis not suliicient to draw down its armature, so that bothbranches of the split circuit remain intact.

Second. Let us suppose now that the line 52, for instance, be signaled,which has its telephone off the hook; but let us suppose that said lineis in other respects in its normal con- (lition. Let it be assumed thatthe operator at 1 5 a. touches its terminal occurring in her section.

The current will pass over the line and splitcircuit, as before, andwill pass to ground through the bell-magnet, receiver, and transmitter.This will energize the line and bell 2o magnet and cause it to draw itsarmature down. The telephone-buzzer a does not respond, for theshunt-circuit of the line is broken at the contact -r and the resistanceof the line 2 cannot be varied by the bell-mag- 2 5 net, so thetelephone-buzzer cannot respond.

Such an indication means that the line is not in its normal condition,which is considered as a busy test- [or the good of the service. It maybe mentioned incidentally that it will have the effect of makingsubscribers place their Suppose, now, that a subscriber presided over bythe operator at c and a subscriber presided over by the operator at ddesires either of the coun ected subscribers, the operators at c and Iwould touch the terminal of either of these circuitswiththeirplugs.Thetwolinesbeingconnected, the resistance would be very much lowered, sothat an increase of current would pass over the lines and through thesplit circuit. This would energize the nn'ignet I and cause said magnetto draw down its armature and break the telephone-buzzer circuit. Thebells of both subscribers would ring and the bellmagnets would be cut inand out of circuit; but this would not be heard in eithertelephone-buzzer r: or (I, for the circuits of these telephones arebroken by the magnets Y. Ye have shown in the drawings in the variousdiagrams the path of the current by arrows and represented the correctposition of parts under the dilierent conditions. 'hen the bell vibrateswehave shown the clapper thereof as provided with two arrows pointed indifferent directions, and when the bell does not vibrate it is shownwithout arrows and as having made one tap and resting against the bell.It will be noted in the third test just described, that while thebell-magnet may be cut in and out as the bell vibrates the combined.conductivity of the two lines, whether the bell be in circuit orshunted, is sufficient to lower the joint resistance to such a degree asto cut out the telephone-buzzer. The condition shown in this case wouldrepresent a case where two subscribers had been talking to each otherand had failed to call oli'that is to say, the call'ing subscriber hasfailed to notify the central office that he is through talking. For thebenefit of the service, when two lines are connected, whetherconversation is being carried on over those lines or not, and whetherthe telephones be on or off the hook, the lines are considered busy.

Fourth. Suppose two lines be connected having both phones off the hook,which would represent the condition of aflairs when two subscribers weretalking to each other. This is represented in the diagram by the lines 441', which are connected at the section B. It now some other subscriberin another section desires either of the subscribers S or 8 connected bysaid lines, the test given will be busy. For instance, if the operatorat d touches the terminal of the line 4 the current will pass over thesplit circuit, as in the last instance, the combined. conductivity ofthe two lines will be such as to increase the current in the branches ofthe split circuit, and will break the telephone-buzzer branch thereof.The subscribers bell will not vibrate, but will make only one stroke andwill be held against the hell by the current passing through thebell-magnet. The shunts in this instance are broken by thetelephone-hooks being raised by the springs, so that the buzzer (1 willnot vibrate, for both shunts are broken and the bells cannot vibrate andcannot therefore cut in and cut out their resistance, so as to cause avibration in the telephone-buzzer, although the circuit of thetelephone-buzzer is not broken in this instance, for it will be noted inthis instance that both transmitters and receivers are in circuit, whichwill so increase the resistance of the lines 4 4', even though they beconnected, that the circuit of the buzzer will be left undisturbed.

Fifth. Suppose, further, that the subscriber S has called for thesubscriber S and the central office has made the connection, but thatthe subscriber S has not yet responded to the call. The telephone ofsubscriber S would be off the hook and the telephone of subscriber Swould be on the hook. This condition of affairs is illustrated by thelines 5 5'. If now, before the subscriber S should respond, anothersubscriber should call for subscriber S say a subscriber presided overby operator at a, and this operator at a should touch the terminal ofthe line 5tl1ere would be in this case an increase of current passingover the lines, for the reason that the resist ance would be lessened bythe conductivity of the two lines. In this instance only one of thetransmitters and receivers in the circuit of the connected lines 5 5, sothat an increase of current will pass through the magnet and break thebuzzer-circuit. The circuit of the telephone-buzzer a would be broken,the armature of the electro-magnet 1 being held away from its contact.The subscribers bell S would vibrate, cutting in and cutting out thebell-magnet; but this would have no influence on the telephone-buzzer d,for the reason that its circuit is broken. The bell of subscriber Swould not vibrate, but make only one tap. The bell-magnet would not becut in and cut out of circuit, for the shunt is broken at r by thetelephone-hook, so that the telephone-buzzer a could not respond to thecondition of line 5 whether its circuit was complete or not. The test inthis instance would be busy, as it should be.

The foregoing cases represent all the conditions of affairs that cantake place, and the correct test by our invention is given in everyinstance. It will be noted that our split circuit could not be used onlywhen the lines had been equalized in resistance to some extent, for if ashort line were signaled over by the split-circuit arrangement anincrease of current would pass through the magnet Z and give the busytest whether such line were in normal condition or not. It will beapparent, therefore, that our split circuit is dependent upon the use ofsome equalizing means. It will also be obvious to those skilled in theart that a split circuit calls for some peculiar form of bell-magnetcircuits, for with some bell-magnet circuits the current would be variedto such a degree as to throw an excessive current into the splitcircuit, and would therefore cause the armature-lever of the bell-magnetto be held away from its stop, or would cause it to chatter, both ofwhich would interfere with the tests.

It will be obvious to those skilled in the art that any other way ofequalizing the circuit can be employed without departing from the spiritof our invention. It will be obvious, also, that other arrangements ofthe bell-magnet circuits may be made and still be within the spirit ofour invention. So, too, other means of breaking the telephone-buzzercircuit when an excessive current is flowing over the wires may be usedand still be within the scope of the invention. So, too, any othersignal-receiving device could be used in place, of the telephone-buzzer.If the lines emanating from the telephone-exchange were all practicallyof the same length, as in small towns, for instance, non-inductiveresistances would be unnecessary. It will be apparent, therefore, thatour invention, while dependent more or less upon equalizing theresistance of the lines, is not necessarily confined to suchresistances. Y

e do not wish therefore to limit ourselves to the exact devices andarrangements set forth, but reserve to ourselves all that which comeswithin the scope of what we now desire to claim and secure by LettersPatent of the United States as our invention, which is around saidbell-magnet made and broken by the armature thereof, and atelephone-hook, also controlling the circuit of said shunt, whereby thecontinuity of the line is always preserved, for the purpose described.

4. A signaling-circuit for the operator of telephoneexchange system inwhich subscribers are signaled from the central office, consisting of abattery suitably grounded or connected with the return-circuits of thesubscribers, a split circuit connected therewith, having atelephone-buzzer or test-instrument in one branch of said circuit, and acircuit maker and breaker forthe first-mentioned branch of said splitcircuit arranged in the other branch thereof, for the purpose described.

5. The combination, with the switch-board, of a telephone-exchangesystem, substantially as set forth, having telephone-lines extendingtherefrom to the various subscribers, a signaling-circuit passing aroundto the operators at the different sections of said switchboard, abattery therefor, a number of split circuits connected therewith inmultiple arc, a telephone-buzzer in one branch of said split circuits, acircuit maker and breaker for the first-mentioned branch of the splitcircuits located in the second branchthereof, and a signaling-plugconnected with said split circuit, substantially as and for the purposedescribed.

6. The combination, in a telephone-exchange system, of a number ofsubscribers wires emanating therefrom, equalizing-resistances for saidlines to make them substan tially uniform in resistance, bell-magnetslocated in said lines in the circuit of the subscribers receivers andtransmitters, and shunts for said bell-magnets controlled by thearmatures of said bell-magnets, for the purpose described.

7. The combination, in a telephone-exchange system, of a number ofindividual subscribers lines emanating therefrom, equalizing-resistancesfor said lines to make them substantially uniform in resistance,subscribers bell-magnets having shunts controlled by the armatures ofsaid magnets, and telephonehooks, also controlling the circuit of saidshunts.

8. The combination, in a telephone-exchange system provided with aswitch-board, substantially as set forth, of equalizing-resistances forthe lines emanating therefrom, a subscribers bell-magnet located in eachof said lines, a shunt therefor controlled by the armature of saidbell-magnet, a telephonehook, also controlling the circuit of saidshunt, a signaling apparatus at the central station, consisting of abattery in electrical communication with the aforementioned lines, asplit circuit connected. therewith having two branches, in one of whicha telephone-buzzer or signal-receiving device is located, a circuitmaker and breaker for said circuit located in the second branch of saidsplit circuit, and a terminal in electrical communication with saidsplit circuit for signaling over said lines.

9. The combination, in a telephone exchange system provided with aswitch-board, substantially a set forth, of a number of subscriberslines emanatingtherefrom, equalizing-resistances for said lines, asubscribers bell-magnet located in each of said lines, a shunt thereforcontrolled by the armature thereof, a telephone-hook, also controllingsaid armature, a signaling-circuit at the central station passingtherearound to each subscriber at the different sections of theswitch-board, a battery therefor with suitable electrical connections,split circuits connected in multiple are With said signaling-circuit andpassing to each operator, a signal-receiving device in one branch ofsaid split circuit, a circuitbreaker for the latter branch of the splitcircuit located in. the second branch thereof, and a signaling-plugconnected with said split circuit, for the purpose described.

10. The combination, in a telephone-exchange system, ofa number ofsubscribms lines emanating therefrom, a sul rscribefis bellmagnet ineach of said lines, a shunt therefor controlled by the armature of saidbell-magn et, a telephone-hook, also con troll ing the circuit of saidshunt, a signaling-eircuit at the central oi'iice, consisting of abattery having; suitable electrical connectitms, one or more splitcircuits emanating" therefrom, in one branch of which a signal-receivingdevice is arranged, and a magnet in the other ln-aneh of said splitcircuit, for the purpose described.

11. A testing means for telephoim-eireuits, embodying, essentially, atest-in stru 1n ent, ci rcuit and battery with suitable electricalconnections, and a cireuit-lnieaker for said testinstrument operated bya predetermined amount of current, whereby when two lines are connectedand the resistance brought to a predetermined value the current will cutsaid test-instrument out of circuit.

In testimony whereof We have hereunto set our hands and affixed ourseals, this 7th day of May, 1888, in the presence of the two subscribinWitnesses.

one. r. DURANT. [n s] HENRY 'L. BAILEY. a]

'Witn esses:

A. G. FOWLER, 'l. GRACE.

